The battery pack is formed as a single unit by covering, with a jacket (hereinafter, also referred to as a jacket for battery pack) such as a heat-shrinkable tube, an assembled battery in which a plurality of cells is electrically connected in series or in parallel. Some battery packs are formed such that a plurality of cylindrical cells is disposed in parallel. FIG. 1 is an external view of a battery pack 91 in which an assembled battery formed by connecting three cylindrical cells (910L, 910M, 910R) disposed in parallel is covered with a battery pack jacket 920. FIG. 2A and FIG. 2B each illustrate an arrangement of the three cells (910L, 910M, 910R) constituting the assembled battery illustrated in FIG. 1 and an electrical connection between the cells (910L-910M, 910M-910R). Hereinafter, the respective cells 910L, 910M and 910R may also be referred to as the cell 910 where it is not necessary to distinguish between them.
As illustrated in FIG. 1, the battery pack 91 is collectively covered with the battery pack jacket 920 formed of a heat-shrinkable tube in a state in which the three cells (910L, 910M, 910R) are disposed in parallel. This maintains the arrangement of the cells (910L, 910M, 910R). FIG. 2A is a perspective view illustrating a body of the battery pack (hereinafter, also referred to as a battery pack body 92) excluding the battery pack jacket 920 from the battery pack 91 illustrated in FIG. 1. FIG. 2B illustrates a state of the battery pack body 92 in the battery pack jacket 920 and corresponds to a plan view when the battery pack 91 illustrated in FIG. 1 is seen from the end surfaces of the cylindrical cells (910L, 910M, 910R).
In the following, a configuration of the battery pack 91 will be described based on FIG. 2A and FIG. 2B. Here, an axial direction 100 of each cylindrical cell (910L, 910M, 910R) is referred to as an up-down direction, and the directions orthogonal to the up-down direction are a right-left direction and a front-back direction. Here, an arrangement direction of the cells (910L, 910M, 910R) is referred to as a right-left direction. Note that, each of the directions of “up-down”, “right-left” and “front-back” is defined as shown in FIG. 2A and FIG. 2B. That is, FIG. 2A illustrates a perspective view when the battery pack body 92 is seen from a right front upper side, and FIG. 2B illustrates a plan view when the battery pack 91 is seen from above.
First, as illustrated in FIG. 2A and FIG. 2B, the three cells (910L, 910M, 910R) are disposed in parallel in the right-left direction. In this example, the three cells (910L, 910M, 910R) are electrically connected in series. Thus, the top and bottom ends of the adjacent cells (910L-910M, 910M-910R) are mutually inverted. Here, in both the right and left cells (910L, 910R), negative terminals 911 face upward, and in the central cell 910M, a positive terminal 912 faces upward (note that, the respective terminals are also collectively referred to as electrode terminals 911, 912 without distinguishing between the negative terminal 911 and the positive terminal 912). On the upper end of the battery pack body 92, the negative terminal 911 of the left end cell 910L and the positive terminal 912 of the central cell 910M are connected via a tab (hereinafter, also referred to as a connecting tab 930) made of a metal plate. On the lower end (not shown) of the battery pack body 92, the negative terminal 911 of the central cell 910M and the positive terminal 912 of the right end cell 910R are connected via another connecting tab 930 (not shown).
The connecting tab 930 is attached to the negative terminal 911 and the positive terminal 912, for example, by welding (spot welding). Furthermore, lead wires (hereinafter, also referred to as power supply lead wires 931) for supplying electric power to external devices are attached to the negative terminal 911 of the right end cell 910R and the positive terminal 912 (not shown) of the left end cell 910L via tabs 932 (hereinafter, also referred to as power supply lead tabs 932) different from the connecting tabs 930.
Further, an axial-type protection element (such as a diode) 940 for preventing overdischarge is connected between the positive terminal 912 and the negative terminal 911 of each cell (910L, 910M, 910R). The protection element 940 is configured such that lead wires (hereinafter, also referred to as element lead wires 942) are guided from both the upper and lower ends of its body 941 along the up-down direction, and leading ends of the element lead wires 942 are connected to the positive terminal 912 and the negative terminal 911, respectively, via the connecting tabs 930 or a dedicated tab 933 (hereinafter, also referred to as an element tab 933). Here, the element lead wires 942 and the power supply lead wires 931 are each connected to the corresponding tabs (930, 932, 933) by solder 934.
Note that the three cells (910L, 910M, 910R) disposed in parallel are held together by insulating adhesive tape 93 to maintain this arrangement. Accordingly, workability when the tabs (930, 932, 933) and the power supply lead wires 931 are attached before the battery pack jacket 920 is attached can be secured, and the element lead wires 942 of the protection element 940 are kept from contact with the battery can which also serves as one of the positive or negative electrodes, so as not to cause an external short-circuit. In order to further reliably prevent the short-circuit, an insulator (insulating tape 94 and a ring-shaped insulator 95 described later) such as adhesive tape is disposed in a region along the element lead wires 942 on the side surface of each cell (910L, 910M, 910R), or on a border between the end surface and side surface of each cylindrical cell (910L, 910M, 910R) and in its vicinity region or the like, as needed.
Furthermore, since the battery can of each cell (910L, 910M, 910R) serves as one of the positive and negative electrodes, the cells (910L, 910M, 910R) themselves are also covered with a cell jacket (not shown). In this example, in addition to the adhesive tape 93, strip-shaped insulating tape 94 extending in a direction along the element lead wires 942 of the protection element 940 is bridged across the side surfaces of adjacent cells (910L-910M, 910M-910R). This prevents short-circuiting as described above, and for example, when the element lead wires 942 generate heat, the cell jacket (not shown) of each cell (910L, 910M, 910R) is prevented from being torn by the heat so that a short-circuit does not occur due to contact of the element lead wires 942 with the battery can. Further, since there is a possibility that the cell jacket (not shown) near the border between the end surface and side surface of each cylindrical cell (910L, 910M, 910R) may be torn by an edge of the connecting tab 930 that bridges the negative terminal 911 and the positive terminal 912 of the adjacent cells (910L-910M, 910M-910R) and a short-circuit caused thereby, a ring-shaped insulator 95 is disposed on the edges between cells (910L-910M, 910M-910R). In this example, the ring-shaped insulator 95 is disposed on the end surface where the projecting positive terminal 912 is located.
When the battery pack body 92 illustrated in FIG. 2A is covered with the battery pack jacket 920 formed of a heat-shrinkable tube, the external shape thereof is more firmly maintained, and the battery pack 91 illustrated in FIG. 1 and FIG. 2B is completed. It should be noted that the configuration of the battery pack is described, for example, in Japanese Unexamined Patent Application Publication No. 2000-340200.
As described above, in the battery pack 91 formed as a single unit by disposing a plurality of cylindrical cells 910 in parallel, when the axial-type protection element 940 is attached, a process of bending the element lead wires 942 of the protection element 940 is required. The protection element 940 has a configuration in which the element lead wires 942 are guided to both ends of the tube-shaped element body 941, and the leading ends of the element lead wires 942 are soldered via the tabs (930, 933) on the end surfaces where the positive terminal 912 or the negative terminal 911 of the cell 910 is disposed. In other words, each element lead wire 942 is bent in the middle of its extension in a direction along the side surface from the end surface of the cell 910. Accordingly, unless the bending shape of each element lead wire 942 and accuracy when the leading ends of the element lead wires 942 are attached to the tabs (930, 933) are strictly managed, a displacement occurs in the attachment position of the protection element 940 and the arrangement of the element body 941. Accordingly, the displacement of the protection element 940 leads to unevenness in external shape and dimension of the battery pack 91. Further, it is necessary to attach the tabs (933, 932) and the connecting tab 930 corresponding to the protection element 940 and the power supply lead wire 931 respectively to the areas of the electrode terminals (911, 912) of the cell 910 which are limited and narrow, and it is difficult to attach a plurality of tabs (930, 932, 933) to one electrode terminal (911, 912) depending on the size of the cylindrical cell 910. Needless to say, the tabs (933, 932) corresponding to the respective element lead wires 942 and the power supply lead wires 931 are required, thus increasing the number of parts. In addition, processes for attaching the respective tabs (933, 932) are also required separately. For this reason, it becomes difficult to reduce manufacturing cost of the battery pack 91.
As described above, the battery pack 91 formed as a single unit by disposing the plurality of cylindrical cells 910 in parallel separately needs a process of winding adhesive tape 93 around the assembled battery constituted by the plurality of cells 910 in the manufacturing process. Even though the adhesive tape 93 positions the cells in place, it is impossible to firmly fix the shape of the cell 910 with the adhesive tape 93, and thus the relative positions of the cells 90 may be displaced due to vibration and impact in subsequent manufacturing processes such as attaching the various tabs (930, 932, 933). If the battery pack 91 is completed in a state in which the positional relationship of the cells 910 is displaced, there is a possibility that this may cause unevenness in external dimension of the battery pack 91, and the battery pack 91 cannot be placed in an electronic device that uses the battery pack 91. On the other hand, if the adhesive tape 93 is tightly wound around the assembled battery to prevent displacement, the adhesive tape 93 is linearly bridged across the V-shaped groove areas, and thus it becomes impossible to place the protection elements 940 into the V-shaped groove areas. Accordingly, when the battery pack body 92 is covered with the battery pack jacket 920, the protection element 940 protrudes markedly from the outer periphery of the battery pack 91. That is, the external shape of the battery pack 91 becomes unnecessarily large.
Moreover, in the battery pack 91, the insulating tape 94 and the ring-shaped insulator 95 are attached in order to protect a cell jacket (not shown) of the cell 910 from the element lead wires 942 of the axial-type protection element 940 and the edge of the connecting tab 930. Thus, it has been difficult to inexpensively provide the battery pack 91 due to the cost related to these members 94, 95 and the process of attaching these members 94, 95.
In view of the aforementioned problems, an objective of the present disclosure is to provide an inexpensive battery pack with no variation in external dimension while securing dimensional accuracy of the battery pack and reducing manufacturing cost by decreasing the number of processes and parts.